Food habits and ontogenetic dietary partitioning of American crocodiles in a tropical Pacific Island in Central America

Seasonal reproduction and feeding ecology of giant isopods Bathynomus giganteus from the continental slope of the Yucatán peninsula

Spatio-temporal trends in the food habits of age-0 lake whitefish

We studied diet and size-related dietary patterns among American Crocodiles (Crocodylus acutus) in marine habitats of coastal Belize (1996–1997). Prey items recovered from crocodile (N = 97) stomach contents included insects, mollusks, crustaceans, fish, amphibians, reptiles, birds, and mammals. Based on an overlapping group analysis of percent occurrence, we concluded that hatchlings and small juveniles feed largely on insects and crustaceans, larger juveniles broaden their diet to include fish and nonfish vertebrates, subadults consume increasing amounts of crustaceans with lesser amounts of insects and nonfish vertebrates, and adults subsist primarily on marine crustaceans. Dietary diversity was uniformly low across all size classes but greatest among small and large juveniles. Conversely, hatchlings, subadults, and adults had the most specialized (least diverse) diet owing to reliance upon a limited selection of prey, largely insects (hatchlings) or crustaceans (subadults and adults). Dietary...

Effect of water temperature on walleye pollock (Gadus chalcogrammus) embryos, larvae and juveniles: Survival, HSP70 expression, and physiological responses

the olfactory organ in small and large juveniles of the tropical yellowstriped reef cardinalfish apogon cyanosoma, collected from the wild (total length [tl] range=17–32 mm, mean=25 mm) was examined by scanning electron microscopy. the olfactory organ consisted of two bilaterally radial rosettes in each fish. they were oval-shaped, located medioventrally, one in each of the olfactory chambers. in small juvenile a. cyanosoma the rosette comprised six lamellae, three on each side of a midline raphe while large juveniles had eight lamellae, four on each side. the lamellae had a continuous cover of cilia, except for the margins. in small juvenile a. cyanosoma (tl mean=24.3 mm) only microvilli were observed, whereas both microvilli and a few cilia, presumably from olfactory receptor neurons, were observed in large juvenile a. cyanosoma (tl mean=32 mm).

Conservation of large predators has long been a challenge for biologists due to the limited information we have about their ecology, generally low numbers in the wild, large home ranges and the continuous expansion of human settlements. The American crocodile (Crocodylus acutus) is a typical apex predator, that has suffered from all of these characteristic problems, especially the latter one. Humans have had a major impact on the recovery of this species throughout its range, even though most of the countries it inhabits have banned hunting. The last decade has made it clear that in order to implement sound conservation and management programs, we must increase our understanding of crocodile spatial ecology. However, in only two countries where American crocodiles have telemetry studies even been published. Herein we have characterized the spatial ecology of C. acutus on Coiba Island, Panama, by radio-tracking (VHF transmitters) 24 individuals between 2010 and 2013, to determine movement patterns, home range, and habitat use. We have then compared our findings with those of previous studies to develop the most comprehensive assessment of American crocodile spatial ecology to date. Females showed a higher average movement distance (AMD) than males; similarly, adults showed a higher AMD than sub-adults and juveniles. However, males exhibited larger home ranges than females, and concomitantly sub-adults had larger home ranges than juveniles, hatchlings, and adults. There was an obvious relationship between seasonal precipitation and AMD, with increased AMD in the dry and “low-wet” seasons, and reduced AMD during the “true” wet season. We found disaggregate distributions according to age groups throughout the 9 habitat types in the study area; adults and hatchlings inhabited fewer habitat types than juveniles and sub-adults. These sex- and age-group discrepancies in movement and habitat choice are likely due to the influences of reproductive biology and Coiba’s precipitation cycle. Juveniles also showed distinct movement patterns and home ranges; however, with sexual maturation and development, these behaviors became more characteristic of adults and sub-adults. Ours is one of a very small number of studies that will allow future management and conservation planning to be based on the comprehensive integration of the spatial ecology of a Neotropical crocodylian apex predator.

We examined interannual variations in the diet of Trachurus japonicus juveniles in relation to prey density and recent 5‐day instantaneous growth rate (IGR) in the southwestern part of the Sea of Japan (SJ) in late spring during 2011–2013. Habitat temperature of juveniles in 2011 was lower than the other 2 years. In all 3 years, more than 97% of juveniles had food in the stomach. Small juveniles <35‐mm standard length (SL) fed mainly on adult female Paracalanus parvus s.l., the most dominant calanoid copepod in the water column, without a significant interannual difference. In 2011 and 2012, large juveniles ≥35‐mm SL predated heavily upon adult female Calanus sinicus which form a high‐energy food for the juveniles. In contrast, in 2013, the large juveniles preyed on a large number of a variety of small‐sized prey items, such as P. parvus s.l., euchaetid copepods, and ostracods. In 2011 when the feeding condition was considered to be favorable, but the habitat temperature was lowest, the IGR of large juveniles was markedly lower than in the other 2 years. Meanwhile, there was no significant difference in the IGR between 2012 and 2013 when the diet composition was markedly different, but habitat temperature was comparable. The present observations indicate that the between‐year difference in juvenile IGR was not explained well by variations in the diet composition. Instead, habitat temperature was concluded to be the more dominant factor causing the observed between‐year differences in the IGR in the southwestern SJ.

Ontogenetic and seasonal diet changes of the juveniles of the marine fish Micropogonias furnieri, a species inhabiting Bahía Blanca estuary (Argentina), were investigated. Two size-related dietary shifts, at 4·00 cm and 7·00 cm total length (LT), respectively, were found. Small juveniles (1·00–3·99 cm LT) ate mostly chaetognaths (Sagitta friderici); medium-sized juveniles (4·00–6·99 cm LT) fed intensively on mysid shrimps (mainly Neomysis americana) and polychaetes, whereas large juveniles (7·00–15·99 cm LT) fed almost exclusively on epibenthic crustaceans (primarily Peisos petrunkevitchi). Increased mouth gape was related to increased size spectrum and mean size of the most important prey items consumed by M. furnieri. Juveniles <510 cm LT ate prey items almost as large as their mouth opening, whereas juveniles >410 cm LT were capable of consuming larger prey items than those found in their stomachs, indicating that the maximum size of prey eaten was not constrained by mouth gape. Seasonal and selectivity dietary analyses showed that M. furnieri can be a highly opportunistic selective feeder. Juveniles relied on S. friderici and P. petrunkevitchi throughout the year, except in summer, when mysids abundance increased in the estuary. Electivity values also showed that prey size and prey relative abundance are important factors in prey selection mechanisms.

Identification of individuals based on morphological patterns is a strategy used primarily in human forensics that has also been applied successfully in several wildlife scenarios. To date, no study has evaluated the potential of these techniques on American Crocodiles (Crocodylus acutus). We assessed whether the dorsal scute number and pattern of 110 American Crocodiles captured from the wild on Coiba Island, Panama could be used for individual recognition. We estimated scute variation using the number and position of scutes, testing both a binary and a coded assessment for scute presence and pattern, respectively. We analyzed scute patterns using 21 transverse scute lines (TSL) including the three most prominent scutes present on each side of the vertebral column axis. We found significant differences in the number of scutes per TSL and longitudinal scute lines (LSL) by individual. Based on both the binary and coded analyses, we identified all American Crocodiles assessed at the individual leve...

The auditory system of the plainfin midshipman fish, Porichthys notatus, is an important sensory receiver system used to encode intraspecific social communication signals in adults, but the response properties and function of this receiver system in pre-adult stages are less known. In this study we examined the response properties of auditory-evoked potentials from the midshipman saccule, the main organ of hearing in this species, to determine whether the frequency response and auditory threshold of saccular hair cells to behaviorally relevant single tone stimuli change during ontogeny. Saccular potentials were recorded from three relative sizes of midshipman fish: small juveniles [1.9-3.1 cm standard length (SL), large juveniles (6.8-8.0 cm SL) and non-reproductive adults (9.0-22.6 cm SL)]. The auditory evoked potentials were recorded from the rostral, middle and caudal regions of the saccule while single tone stimuli (75-1,025 Hz) were presented via an underwater speaker. We show that the frequency response and auditory threshold of the midshipman saccule is established early in development and retained throughout ontogeny. We also show that saccular sensitivity to frequencies greater than 385 Hz increases with age/size and that the midshipman saccule of small and large juveniles, like that of non-reproductive adults, is best suited to detect low frequency sounds (<105 Hz) in their natural acoustic environment.

Most research on ontogenetic niche shifts has focused on changes in habitat or resource use related to food resource distribution and heterospecific size‐limited predation. Cannibalism, an intraspecific interaction, can also affect habitat selection or resource use by vulnerable size classes. Morphological defenses, such as spines, increase the effective size of an individual, making it more difficult to consume. The importance of such defense structures in affecting niche shifts in early life history stages is unclear. Using a combination of field observations and experiments in aquaria and wading pools, we examined the relative roles of cannibalism and morphology in determining juvenile habitat use in two populations of threespine stickleback that differ in pelvic spine morphology. Juveniles were categorized into three size classes: small (5–10 mm), medium (11–15 mm), and large (15–25 mm). In experiments assessing the relative vulnerability of juveniles to cannibalism by adults, we documented a significant difference among size classes in the number of juveniles eaten such that more large juveniles were eaten from the population lacking pelvic spines. The natural distribution of small and large juveniles in two distinct littoral microhabitats, open water and vegetation, was determined in each lake. In both populations, small juveniles were more abundant in vegetation. In the population with pelvic spines, a greater proportion of large juveniles was observed in open water than in vegetation. In the population without pelvic spines, the proportion of large juveniles did not differ between the two habitats. Experiments comparing juvenile habitat use in the presence or absence of adult conspecifics suggest that differences in habitat use may not only depend on the size of the individual, or the size of the individual relative to the size of the adult predator, but also on the degree of development or expression of defensive structures.

Reliable estimates of crocodylian population size are desirable for both understanding the ecology and natural history of species and developing sound conservation and management plans. However, choosing appropriate methods to estimate population numbers can be difficult due to the paucity of comprehensive analyses regarding their effectiveness, robustness, and applicability. We estimated the American crocodile population size in the southern tip of Coiba Island, Panama, using both spotlight surveys (Messel's and King's visible fraction estimations) and mark–recapture (POPAN formulation–superpopulation) methods. We assessed and compared the outcomes of these methods with the overall capture record for the study area from 2009 to 2013, evaluating their applicability, accuracy, strengths, and limitations. Using historical and current capture data, we defined a minimum population size of ~112 non‐hatchling animals in our study area, which was larger than both Messel's (19.00 ± 7.50 individuals) and King's (25.71 ± 7.25 individuals) population size estimates, revealing that these latter approaches clearly underestimate population numbers. We estimated a total population size that range between 147 and 257 individuals based on POPAN formulation grouping the data by sex and age groups as the most plausible population size of the American crocodile population in this area at the time. We analyzed and discussed sources of bias in population size estimations for all methods used in the present study, providing recommendations to minimize errors and improve estimations. Finally, we analyzed and compared population ecology attributes obtained in our study with what have been reported in other insular and coastal areas across the American crocodile range, increasing knowledge about the ecology of the species.

Effects of geographic origin on growth and food intake in Eurasian perch ( Perca fluviatilis L.) juveniles under intensive culture conditions

Shortage of natural crevice shelters may produce population bottlenecks in juvenile Caribbean spiny lobsters (Panulirus argus), a socially gregarious species. We conducted a field experiment to test enhancement of a local population of juvenile P. argus with the addition of artificial shelters ("casitas") that mimic large crevices (1.1 m(2) in surface area and 3.8 cm in height). Changes in density and biomass of juvenile lobsters 15-50 mm carapace length (CL) were assessed with a multiple before-after control-impact (MBACI) analysis. Separate analyses were also conducted on small (15-35 mm CL) and large (35.1-50 mm CL) juveniles to assess size-related effects. First, we carried out 13 lobster surveys on nine fixed 1-ha sites over a shallow reef lagoon ("before" period). Then, we deployed ten casitas in each of five sites and left four sites as controls, and conducted 22 further surveys ("after" period). Deployment of casitas resulted in a sixfold increase in juvenile density (76% contributed by small and 24% by large juveniles) and a sevenfold increase in biomass (40 and 60%, respectively). Capture-recapture results revealed that enhancement was achieved not by promoting individual growth but by increasing survival, persistence, and foraging ranges of small and large juveniles. Casitas both mitigated shortage of natural shelter and increased sociality, allowing for cohabitation of smaller, more vulnerable juveniles with larger conspecifics that have greater defensive abilities. Casitas may help enhance local populations of juvenile P. argus in Caribbean seagrass habitats, typically poor in natural crevice shelters. The use of MBACI and the simultaneous assessment of multiple interrelated response variables may be a powerful analytical approach to test shelter limitation in other species and to examine the function of structural habitat in other systems.

Abstract. We assessed the reproductive ecology of the American crocodile (Crocodylus acutus) on Coiba Island, Panama from January–December 2013. We examined nest site characteristics from January–April and hatchling survivorship from April–December. Ten nests were examined at three nesting localities where 30% of the nests were found under forest canopies and 70% were exposed to sunlight (distance to nearest tree = 280 ± 110 cm). Half of the nests were built closer to the sea and the other half closer to bodies of freshwater (700 ± 360 cm). The nest dimensions were 17.5 ± 7.8 cm from the top of the clutch to the surface, 42.9 ± 9.9 cm from the bottom of the clutch to the surface, and 35.9 ± 3.6 cm wide at the top of the nest cavity. The average soil conditions in the nests consistently had high concentrations of potassium (69.3 mL/L) and manganese (9.2 mg/L), moderate concentrations of phosphorus (6.6 mg/L) and iron (3.7 mg/L), and low concentrations of zinc (0.5 mg/L) and copper (0.0 mL/L). Cation exchan...